The invention relates to a control valve for a fuel injection valve, having a valve needle that is displaceable in a control chamber that is provided with an inlet, an outlet, and a valve seat.
One such control valve is known from German Patent Disclosure DE 197 27 896 A1, for instance, and serves to bring about the opening of a nozzle needle of the injection valve in order to inject fuel into a cylinder of an internal combustion engine.
The nozzle needle is acted upon continuously with an opening pressure that seeks to lift the nozzle needle away from the associated valve seat. This opening force counteracts a closing force that is generated in a control pressure chamber. As long as the pressure in the control pressure chamber is kept at a high level, the closing force generated there is higher than the opening force acting on the nozzle needle, and thus the nozzle needle remains closed. Conversely, if the pressure in the control pressure chamber and consequently the closing force generated there drop, then the opening force succeeds in lifting the nozzle needle away from the valve seat. Fuel can now be injected.
The pressure in the control pressure chamber is controlled by the control valve, by opening or closing an outlet. If the medium, typically fuel, delivered to the control pressure chamber is dammed up by closure of the outlet, then a high pressure is generated in the control pressure chamber and keeps the nozzle needle in a closed state. If conversely the control valve opens the outlet, the pressure in the control pressure chamber drops, so that the nozzle needle can open.
The control valve according to the invention has an advantage that at little expense, two different open states of the control valve can be attained, namely a partly open state, in which the fluid can escape from the control pressure chamber through the throttle bores, and a fully open state, in which both the throttle bores and the outlet conduit are open. The switchover between these two open states is effected solely by controlling the stroke of the valve needle. In this way, different types of injection can be attained.
In a preferred embodiment of the invention, the valve needle is provided with a needle head, which is larger than the inside diameter of the throttle ring, and the throttle ring is disposed between the needle head and the valve seat. Is this version, the valve needle serves not only for switching but also simultaneously as a guide for the throttle ring. The throttle ring is retained firmly in the axial direction between the needle head and the valve seat.
It is preferably also provided that a spring that urges the throttle ring away from the valve seat toward the needle head is disposed in the control chamber, and that a stop for the throttle ring is provided in the control chamber and limits the stroke of the throttle ring away from the valve seat. By means of the spring, the throttle ring can be displaced in an especially simple way in the interior of the control chamber, without requiring a separate actuating element controlled from outside. Also with this version, a partly open state of the control valve can be attained that is maximally independent of positional tolerances of the valve needle. Specifically, a tolerance range can be established within which the throttle ring is already lifted from the valve seat but has not yet struck the stop. Within the entire tolerance range, an outflow cross section through the throttle bores is obtained that is virtually independent of the position of the valve needle in this partly switched state.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing.